1. Field of the Invention
This invention relates to identification, location, and telemetry systems, and more particularly, to a system for positively identifying and receiving telemetry from devices on assets and individuals using reduced power and reduced channel occupancy.
2. Description of the Related Art
Identification, location and tracking systems identify the presence, the absence, or movement of unique devices affixed to people and objects within a predefined area. These systems find increasing application in all areas of automation, accounting, manufacturing, and materials handling areas as well as medical facilities and other areas where real time location ant identification can be critical.
In a typical system, one or more objects or individuals are provided with transmitting devices, commonly known as "TAGs," which can be tracked by an array of receivers in a given tracking area. Each TAG periodically traits a unique digital identification number which is sensed by one or more receivers. The receiver information is then forwarded to a data processing system for storage and tracking. A number of systems have been developed using various techniques, such as radio frequency (RF), and ultrasound for continuously tracking location.
Such systems typically employ radio frequency or ultrasonic based transmitters and sensors. RF systems can provide a high degree of accuracy while maintaining a comparably favorable ratio of range per watt of power. A system using RF tracking methods is disclosed in U.S. Pat. No. 5,119,104 to Heller, which is hereby incorporated by reference. The Heller patent discloses a system which addresses some of the issues associated with RF tracking systems. As disclosed, radio frequency transmissions can be susceptible to interference from multipath reflections, as well as signal attenuation through certain objects which tends to distort the accuracy of the location data. The Heller patent offers a method for incorporating a plurality of receivers and time-of-arrival data to more accurately identify target location.
The Heller patent also offers power conservation by including a motion detector with each TAG transmitter. By transmitting identification information when the target is in motion, but reducing transmissions when motionless, the system can conserve power during motionless periods. The receiving system simply uses the last recorded transmission to identify location. However, one power consumption issue of that system is that if the object is moving, the system of the Heller patent does require higher power consumption for more frequent transmissions.